Humulinic Acids Research Articles

Molecular mechanisms behind the antimicrobial activity of hop iso-α-acids in Lactobacillus brevis

The main bittering component in beer, hop iso-α-acids, have been characterised as weak acids, which act as ionophores impairing microbial cells' function under acidic conditions as present in beer. Besides medium pH, divalent cations play a central role regarding the efficacy of the antimicrobial effect. The iso-α-acids' non-bitter derivatives humulinic acids can be found in isomerised hop extracts and can be generated during hop storage. Therefore, they have been under investigation concerning their influence on beer sensory properties. This study sketches the molecular mechanism behind iso-α-acids' antimicrobial activity in Lactobacillus (L.) brevis regarding their ionophore activity versus the dependence of the inhibitory potential on manganese binding, and suggests humulinic acids as novel tasteless food preservatives.We designed and synthesised chemically modified iso-α-acids to enhance the basic understanding of the molecular mechanism of antimicrobial iso-α-acids. It could be observed that a manganese-binding dependent transmembrane redox reaction (oxidative stress) plays a crucial role in inhibition. Privation of an acidic hydroxyl group neither erased ionophore activity, nor did it entirely abolish antimicrobial activity. Humulinic acids proved to be highly inhibitory, even outperforming iso-α-acids.

PREPARATION, PURIFICATION AND SEPARATION BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF HUMULINIC ACIDS, DEHYDROHUMULINIC ACIDS, AND HULUPONES

Modification of published procedures are described for the preparation of humulinic acids, dehydrohumulinic acids and hulupone, using iso-α-acids as starting material. These procedures provide facile routes for preparation of these compounds in higher yields than was hitherto reported, and also in sufficient purity for their use as standards in quantitative High Performance Liquid Chromatography. An alternative and more feasible route to hulupones, using β-acids as starting material, is also outlined.

Separation of Humulinic Acids by Reverse-Phase High Performance Liquid Chromatography

High performance liquid chromatography (HPLC) is finding greater use in the brewing industry for the analysis of hop compounds. The present work extends the previously developed solvent system of methanol, water, and tetrahydrofuran used on a commercially available reverse-phase column to the separation of humulinic acids and the oxidation products of isohumulone. The powerful capabilities of HPLC, as used to monitor several reactions of hop compounds to humulinic acids under various conditions, are demonstrated.

Separation of Humulinic Acids by Reverse-Phase High Performance Liquid Chromatography

Separation of Humulinic Acids by Reverse-Phase High Performance Liquid Chromatography

OXIDATIVE DEGRADATION OF ISOHUMULONES IN RELATION TO FLAVOUR STABILITY OF BEER

Isohumulones undergo oxidative degradation in bottled beer during shelf storage to give volatile compounds including 2-alkanones with chain lengths of C3 to C11, alkanals with chain lengths of C2 to C10 2-alkenals of C4 to C7 or more and 2,4-alkadienals of C6 to C7. Since some resultant aldehydes are involved in the formation of stale aldehydes, very high levels of isohumulones in beer may cause considerable staling of beer flavour. Isohumulones were decomposed to these carbonyl compounds more easily than their derivatives, such as di- or tetrahydroisohumulones and humulinic acids, because the double bond or carbonyl group of the isohexenoyl side chain of the isohumulone molecule is involved in this degradation. This oxidation of isohumulones was greatly suppressed by addition of 300 ppm of sodium ascorbate or 40 ppm of ferrous ion.

Stepwise Elution of Hop Resin Constituents from QAE Sephadex A-25 Ion-Exchange Resin

A method was developed for the chromatographic separation of hop constituents by stepwise elution. A column of QAE Sephadex A-25 acetate was used with different concentrations of acetic acid in 80% methanol:water (v/v). The separated constituents included the β-acids, α-acids, humulinic acids, iso-α-acids, and hulupones. Results obtained were comparable to those from gradient elution in accuracy and precision. Resolution was improved, particularly for the separation of β-acids from the less acidic unidentified substances. Stepwise elution eliminates the need for automated gradient elution equipment.

Studies in organic mass spectrometry—XI. The fragmentation of hop bitter acids derivatives having a five membered ring structure

AbstractThe mass spectra of the hops derived humulinic acids, isohumulones and hulupones are discussed. The fragmentations are in accordance with those found for model compounds.

GUSHING PROMOTERS AND SUPPRESSANTS IN BEER AND HOPS

The fatty acids present in beer and hops were found to have pronounced effects on gushing, some at concentrations of I ppm or less. Saturated fatty acids are weak gushing promoters, while unsaturated acids are powerful suppressants. A parallel structure-activity correlation also exists in a series of α-acid derivatives and their analogues. Compounds with the unsaturated side-chains intact showed either weak suppressant activity or none at all. Loss of carbon-carbon unsaturation through hydrogenation or cyclization produced powerful gushing promoters, but reduction of carbonyl unsaturation as in ρ-isohumulones, or loss of side chains as in humulinic acids had no effect on gushing. Promoter and suppressant effects of the compounds tested were non-specific and mixtures of unsaturated fatty acids suppressed all instances of gushing, whether natural or artificially induced. The results indicate that beer normally contains both gushing promoters and suppressants, and gushing may sometimes be due to an imbalance between them.

Circular dichroism—LI : Circular dichroism of derivatives of hop constituents containing a five-membered ring

The conformation of the cyclopentenones 5 to 8 is determined from their CD-spectra. The site of enolization and the conformation of cis- and trans-isohumulone ( 1 and 2) is determined with the help of the CD-spectra, the direction of enolization for the humulinic acids 3 and 4 is tentatively determined by the same method.

Humulinic Acids: IX. Formation and Isomerization

AbstractThis paper discusses the formation and isomerization of humulinic acids and the origin of positive and negative optically active trans humulinic acid in humulone hydrolysis mixtures. The separation of the cis humulinic acid stereoisomers is described.

The absolute configuration of the isohumulones and the humulinic acids

The absolute configurations for the trans and cis diastereoisometric isohumulones (II) and humulinic acids are determined (III). This is achieved mainly by reductive transformation of III into the dihydrodeoxohumulinic acids (IV), and application of the Horeau method. Trans isohumulone is the S(C-4) S(C-5) form and cis isohumulone the R(C-4) S(C-5) form.

Humulinic Acids. X. The Hydrogenolysis of Humulinic Acids

Humulinic Acids. X. The Hydrogenolysis of Humulinic Acids

HUMULINIC ACIDS. VIII. STEREOISOMERS OF HUMULINIC ACIDS

Humulinic acid contains chiral centra at C4 and C5 and can therefore theoretically occur in four optically active stereoisomers. The diastereoisomeric forms are at the same time trans and cis isomers of each other (formerly humulinic acids A and B).5 This paper concerns the isolation and characterization of the trans and cis co- and ad-humulinic acids and the separation of racemic trans humulinic acid in its enantiomorphs.

4-ACETYL HUMULINIG ACIDS

4-Acetyl humulinic acids A and B have been separated by countercurrent distribution from the reaction products obtained by boiling humulone in alkaline solution. Structures are postulated for the two compounds which are consistent with their spectral and chemical characteristics.

The humulinic acids VI. Dihydro‐, dihydrodeoxo‐ and further hydrogenated derivatives

AbstractThe hydrogenation products of humulinic acids A and B are described and mechanisms for the reactions are advanced. The isolated 2, 4‐diisopentylcyclo‐pentane‐1, 3‐dione (X), trans‐ 1, 3‐diisopentyl cyclopentane (XV) and 2, 5‐diiso‐pentyl‐2‐cyclopenten‐1‐one (XII) have probably not been isolated before.

The humulinic acids. V. Specific catalytic reductions methyl allohumulinic acid D.

AbstractMethyl allohumulinic acid D (I) was isolated after acid treatment of either humulinic A (HAA) or humulinic acid B (HAB). Some specific reductions on this and other humulinic acids are reported. Dihydromethylhumulinic acid D (IV) is described. A new route to dihydro‐HAB was developed.

The isomerization products of humulone

AbstractThe substance known as “isohumulone” is in fact a mixture of four components. They were separated by C.C.D. According to a new nomenclature based mainly on the chemically related humulinic acids A,B, C etc. series they are the stereoisomers isohumulone A and B (IV and V) and alloisohumulone A and B (VI and VII).

223. Chemistry of hop constituents. Part XXIII. The structure of humulinic acid C and other acid-transformation products of humulinic acids

223. Chemistry of hop constituents. Part XXIII. The structure of humulinic acid C and other acid-transformation products of humulinic acids

The Humulinic Acids II. Hydrogenation products. Chemical evidence for the structure of humulinic acids A and B

AbstractChemical evidence shows that humulinic acids A and B (1) are cis‐trans isomers, corresponding to structure I and II or vice‐versa.

The Humulinic Acids IV. Humulinic acids C, D.

AbstractHumulinic acids C and D have respectively stucture III and IV. The methyl derivative of HAD(2) has structure V. The assignments are based on physical and chemical evidence. A mechanism for the formation of these substances is advanced.The preparation and isolation of a number of humulinic acid isomers or derivatives called humulinic acids A, B, C, D (HAA, HAB, HAC, HAD) was reported by us before (2). The structure elucidation of humulinic acids A and B showing them to be trans and cis isomers I and II was also reported by our laboratory (1). The recent structure attribution to humulinic acid C by English authors (3) prompts us now to publish our further results.